For cylindrical reflectors having a circular or modified parabolic profile, the concentration of direct solar radiation for achieving high temperatures is normally accomplished by control systems which line up the reflectors so as to focus the energy on a collector located along the line of focus of the associated reflector. Generally, the systems used for maintaining the proper alignment of the solar device as the sun's elevation changes have been complex and expensive. The overall efficiency of the collection of radiant energy from the sun is, among other things, governed by the amount of energy actually collected, compared with the energy and expense required for its collection. The stationary energy absorber is one which is generally positioned to receive maximum radiation at noon and is not provided with any scheme for tracking the sun. Hence, maximum solar energy collection is sacrificed to avoid the expense and energy of a tracking scheme. On the other hand, energy absorbers such as heliostatic devices which are provided with mechanical means for following the sun, usually are timed, motor-driven devices, and have increased solar collection capabilities, but are more expensive because of the tracking system. This increased expense of prior art tracking means is particularly prohibitive where small individual units are desirable, such as in underdeveloped countries or in household use, where a simple durable solar energy collection device is necessary.
In a publication entitled "Stationary Mirror Systems for Solar Collectors", by H. Tabor which appears in Solar Energy, Vol. 2, Nos. 3-4, July-October 1958, at pages 27-33, there is defined an angle in solar geometry called the East-West Vertical (EWV) altitude. This is the angular movement related to the rise and fall of the sun. It is both a daily and annual phenomenon; that is, it varies throughout the day and throughout the year. It is a function of both latitude and season. The correct position of a solar collector to account for the variations of EWV altitude is usually limited to variations in the seasonal tilt of the collector in accordance with seasonal changes in the declination angle for the sun. The EWV altitude, which is a relatively small, angular movement, is to be distinguished from the large angle the sun traverses over the course of a day as it sweeps the sky from sunrise to sunset. For purposes of designing a solar device, we consider that, at the equator on June 21, the sun is over the tropic of cancer which is about 24.degree. north of the equator. Hence, the daily EWV angle is 90.degree.+24.degree.=114.degree.. This is about the maximum required angle on earth through which a solar collector device is required to operate.
In cylindrical radiant energy collectors, such as described in a publication by Roland Winston appearing in Solar Energy, Vol. 16, No. 2, at pages 89-95 and in his U.S. patent titled "Radiant Energy Collector", U.S. Pat. No. 4,002,499, the collector configuration is determined by the angle of acceptance. The concentration factor is roughly inversely proportional to this angle so that the greater the acceptance angle, the less the concentration, but the longer the period of collection for solar collectors. Therefore, if a collector could be provided with means which would allow a reduced angle of acceptance without a decrease in the period of collection, a higher concentration in a simplified design of the collector would be achieved. In U.S. Pat. No. 4,044,752, to A. Z. Barak, entitled "Solar Collector with Altitude Tracking", a device is described which provides for turning a solar collector about in an east-west horizontal axis so that the collector is tilted toward the sun as the EWV altitude of the sun varies each day. This invention only provides for a step change between two to three positions, and is not intended to track the sun as it sweeps the sky from sunrise to sunset, but only to tilt the collector in one of two or three discrete positions, towards the sun as the EWV altitude of the sun varies each day.
In U.S. Pat. No. 3,982,526, also to A. Z. Barak entitled "Turning Collectors for Solar Radiation", a device is provided for turning a solar collector about the polar axis so that the collector is directed towards the sun and sweeps from east to west as the sun tracks the sky each day. This patent provides no specific compensation for EWV altitude and only provides for the collector to turn between two stable states, that is, it does not provide continuous alignment of the collector with the sun. Also of interest is U.S. Pat. No. 3,213,285, issued to T. J. McCusker on a heliotropic orientation mechanism. That device employs bimetallic sensing strips or liquid capillary sensing means as thermomechanical positioning means. The device is intended for extraterrestrially located collectors and is incapable of supplying adequate forces for practical terrestrial use. Also, as a result of the support configuration between the collector and the bimetallic strips, the total deformation of the collector alignment mechanism is limited to perhaps 20.degree. (see FIG. 2 of the patent).
None of these prior art devices provide for simple, durable collector alignment mechanisms capable of 180.degree. of rotation (or at least 114.degree. as explained above) and capable of tracking the sun continuously as it sweeps the sky and as it seasonally and daily changes its EWV altitude.
It is, therefore, an object of this invention to provide an improved solar collector alignment means.
A second object of this invention is to provide means for continuously varying the tilt of the solar collector around its horizontal axis in response to the daily and seasonal changes in the sun's EWV altitude.
A third object of this invention is to provide means for rotating the solar collector around its vertical axis so as to face the sun continuously during its sweep of the sky from sunrise to sunset.
It is a further object of this invention to provide a collector orientation device that corrects misalignment of the solar energy collector with no external power consumption.